Preparation for Mixing

[ LiB ]

Before you begin mixing there are several steps you must take in order to be prepared. Depending on what type of mix you are creating, whether a stereo or surround mix, there are several considerations to be made regarding speakers , their placement, and with the input and output configuration of your Pro Tools mixer.

The I/O Setup

The I/O Setup in Pro Tools is a very helpful section that is often overlooked (See Figure 8.1). Choose Setups > I/O Setup to access this feature. Here you can create custom names for different inputs, outputs, and even buses that you would use for certain purposes. For instance, the first six outputs of your system can be labeled as 5.1 Surround Mix. The next pair could be called Pro Logic Stereo, and so on. Now, each time you select an output for a specific track, Aux send, or Master fader, you will see 5.1 Surround Mix and Pro Logic Stereo as available options. It is possible to label all your inputs and hardware inserts with the devices that are connected to them, such as Line 1, Synth 3, Plate Reverb L, and so on.

Figure 8.1. The I/O Setup. Here you can create custom names for inputs, outputs, hardware inserts, buses, and mic preamps connected to your system.

Outputs

When mixing in surround, labeling of outputs and buses is more important because of the complexity of the surround mixer. In order to be able to use the surround capabilities of the Pro Tools mixer, you must first create a surround sound output or bus that a track can be assigned to. Figure 8.2 shows the pull-down menu where you can determine what types of output paths are available.

Figure 8.2. The Output To Path Type pull-down menu. This menu determines what type of output path you are creating, whether Stereo or 5.1 surround.

Create a 5.1 output path and call it 5.1 Surround Mix. Assign different hardware outputs of your system to the different channels of the surround path, as shown in Figure 8.3. This will determine what physical outputs of your system will be connected to each speaker in your playback system. You will have to deactivate any other output path that overlaps the outputs used in this new surround path.

Figure 8.3. Assigning physical outputs to members of an output path.

It is also possible to create a sub-path within the surround path itself. For instance, you might want to create a sub-path that is just the stereo left and right speakers. This allows you to assign tracks to just the stereo speakers. This can help conserve DSP and also simplify your mixer. A mono sub-path for the center channel speaker makes it easy to assign dialog tracks to just the center channel. Figure 8.4 shows the two sub-paths that have been created underneath the 5.1 Surround Mix.

Figure 8.4. Creation of stereo and mono sub-paths allows signals to be routed directly to the center channel or the left and right speakers discretely.

When assigning outputs for a track, you will be given the option to select 5.1 Surround Mix, Stereo, or Center CH. Depending on the track you are working with, one of these choices will be most appropriate.

Buses

Buses can also be grouped together to create multi-channel pathways . These can be helpful when combining large numbers of related tracks to form a mix sub- group that will be used to create a mix "stem." Figure 8.5 shows the formation of a 5.1 surround bus for effects. All the effects tracks can be routed to this bus and maintain their positions in the soundfield. This helps in mixing later, when you want to balance levels between dialog, foley, effects, and music. If each group of sounds is routed together on its own bus, balancing their respective levels is as simple as grabbing one fader. Later in this chapter, I will talk more about grouping channels and creating mix stems this way.

Figure 8.5. Creating surround buses for sub-grouping related sounds together in a surround configuration.

NOTE

MIX STEMS

Mix stems are finished master recordings made from a post-production mix session. A stem is created for each facet in the production: dialog, foley, effects, and music. These stems can then be combined at unity gain to create the different print masters for each format the project will end up on: Dolby Digital, Dolby Pro Logic, and even foreign language versions that do not include dialog tracks.

Inserts

It is possible with Pro Tools to patch in your favorite external hardware processors on channels in the same way that you use plug-ins. Each channel of external processing requires an I/O pair from your Pro Tools hardware. Keep in mind that when mixing in surround, at least the first six outputs of your hardware will be used for monitoring only. These outputs, and their corresponding inputs, will not be available for external inserts.

Let's say you want to patch an external reverb that has a unique sound you would like to use in your Pro Tools mix. Assuming that this reverb unit is stereo in and stereo out, you will need two I/O pairs to patch the unit in. Since I use an ADAT Bridge in my system, I will use that as an example. The ADAT Bridge is connected to two 8-channel AD/DAs for a total of 16 I/O pairs. The first six outputs are connected to my monitoring setup. Here's how to patch the reverb unit in I/O pairs 7 and 8 and create a hardware insert for it.

Physically connect outputs 7 and 8 to the left and right inputs of the reverb unit.
Connect the left and right outputs of the reverb units to inputs 7 and 8.
Choose Setups > I/O Setup.
Click the Inserts tab.
If there are no inserts already created, click New Path.
As this is a stereo reverb unit, select Stereo from the pull-down menu, as shown in Figure 8.6.

Figure 8.6. Creating a stereo insert path in the I/O Setup.
Double-click in the Name field and enter the name for your stereo reverb unit.
Select the appropriate I/O pairs that are connected to the reverb. In this case, ADAT A, channels 7 and 8.
Go to any stereo channel or aux in your mixer and click on an insert button. You will now be able to go to the Insert submenu where you'll see the reverb unit listed as an insert, as shown in Figure 8.7.

Figure 8.7. The reverb unit is now available as an insert on any channel. It will function like a plug-in. However, it can only be used once in any mixer configuration.

NOTE

INSERT LATENCY

Understand that when you program a hardware insert and use it on any track, aux channel, or master fader, a certain amount of latency will be induced into that channel. On TDM Mix systems, this amount is 96 samples. That might seem small, but it can wreak havoc on the phase relationships of different signals in a mix. Latency will be covered later in this chapter.

Now that you have set up your input and output configurations, it is time to connect the speakers to your monitoring system and calibrate them for ideal listening.

Speaker Systems and Layouts

Depending on what type of format you're mixing, the speakers' size and relative positions to your ears are very important. If you are mixing music that is going to be heard in cars or on small portable radios, smaller speakers will help you achieve the best results. If you're mixing for home stereo listening, larger, full-fidelity speakers will be appropriate. If you're mixing for a home-theater system with four or perhaps six different speakers including a subwoofer , having a similar setup in your mix room will help you achieve the best results. Finally, if you're mixing for a theatrical presentation, being able to listen to the actual type of system that is found in theaters will help you get a realistic idea of what your mix will sound like in its final form. In any situation, proper alignment and test level calibration will help you achieve the best results.

Mixing in Stereo

The main consideration when mixing in stereo is the proper angle between the two speakers in your listening position. The standard is a 60-degree angle from the left speaker to the right speaker, as shown in Figure 8.8. While placing the speakers at a wider angle can be effective, loss of the phantom center image might be the result of placing the speakers too far apart. Angles of up to 90 degrees can be used effectively if the acoustic treatment in the control room is sufficient to maintain a strong center image.

Figure 8.8. A diagram of the standard stereo speaker configuration using a 60-degree angle. X is the distance between the listener and each speaker.

You can set up this type of monitoring configuration using a tape measure. If the distance between the listener and each speaker is the same as the distance between the speakers themselves , you will have created a 60-degree angle between the speakers. This forms an equilateral triangle between the listener and the two speakers, and will allow you to effectively hear signals in the stereo field. The stereo image you create should remain intact when played back on many other types of systems.

Mixing in 5.1 Surround

5.1 Surround is the most common form of surround mixing being done today. It's used in theatrical presentation, DVD releases, and in HDTV broadcasts. The basic equilateral triangle that is used for stereo mixing forms the basis for the 5.1 Surround setup. Four additional speakerscenter, subwoofer, left surround, and right surroundare then added to the stereo pair.

The Center Channel

It is often said that the center channel is primarily used for dialog, and while it is true that its proximity to the center of the screen makes it the most appropriate location to put dialog, this channel is also a primary carrier of key sound effects. Also, people in the audience who might not be sitting towards the center of the room will still perceive dialog coming from the center channel as being very closely tied to the center image on screen. The center channel should be placed so that it is aligned with the center of the screen, as shown in Figure 8.9.

Figure 8.9. The center channel speaker should be aligned with the exact center of the viewing screen. If possible, all three speakers should be on the same horizontal planethat is, level with each other.

Sometimes, for practical reasons, the three front speakers cannot be on the same horizontal plane. In order to accommodate a convenient screen location, the center speaker will often be lowered so as not to be in front of the screen. When this is necessary, you must endeavor to keep the tweeters of all three speakers as aligned as possible. Figures 8.10 and 8.11 show two common alternatives for center-channel placement when accommodating a large viewing screen.

Figure 8.10. Placement of the center channel speaker. Notice that the distance from each speaker to the listener is the same, placing all speakers on an arc in front of the mix position. This keeps all signals phase- coherent or arriving at the same time.

Figure 8.11. Here, the center channel speaker has been placed on its side in order to lower it to accommodate the viewing screen. If possible, the left and right speakers should be lowered somewhat to maintain alignment with the high-frequency driver of the center channel speaker.

Stereo creates a phantom center image by having equal volumes of a signal in both the left and right speakers (panned in the middle). In a large viewing room, audience members located off to one side of the room will perceive a shift in that phantom center image that will disassociate the dialog from the images on-screen. The center channel speaker eliminates this problem. Only in very limited circumstances will you hear dialog elements in either the left or the right speaker. These cases are primarily instances when a character enters from the extreme left or right of the film frame while talking.

The center channel speaker should be placed equidistant from the listener, the same as the two left and right speakers. This places the front three speakers on an arc in front of the listener, as shown in Figure 8.10.

Take care to keep each speaker equidistant from the mix position. This keeps signals phase-coherent from all speakers, allowing accurate level and pan information to reach the listener. If the center channel was to be placed forward of this position to accommodate a monitor or viewing screen, signals coming from it would arrive at your ears earlier than signals emanating from either the left or right speakers. If this happens, sounds that pan across L-C-R may not follow a smooth movement. Phase coherence between all speakers in a surround sound setup is critical for accurate monitoring. If the center speaker must be a different distance than the left and right speakers, compensating time delays may be used to achieve coincident arrivals.

The viewing screen often becomes an obstacle for placement of a center channel speaker. There are several options that will allow for accurate monitoring while still giving space for a sizable viewing screen. The center channel speaker may be tilted on its side 90 degrees in order to be lower and more out of the way, as seen in Figure 8.11. The center channel speaker may be inverted and placed over the viewing screen in some situations. When this is done, be sure to make every attempt to align the high-frequency drivers in each speaker in the same horizontal plane, as shown in Figure 8.12. This allows for a more seamless soundscape. Figure 8.13 shows the optimal position for the center channel speaker in the same horizontal plane as both left and right speakers.

Figure 8.12. In this setup, the center channel speaker has been inverted and placed above the viewing screen. Notice that the left and right speakers have been raised in an attempt to align high-frequency drivers in the same horizontal plane.

Figure 8.13. The optimal position for the center channel speaker is in the same horizontal plane as both the left and right speakers.

Surround Speakers

Surround speakers are intended to provide an immersive experience by creating a 360-degree soundfield in which the listener is placed. In order to provide such an encompassing soundfield, these speakers must be placed behind the listener. ITU-R specifications outline the position as 110 degrees off axis from the center channel speaker position and equidistant from the listener. Figure 8.14 shows the complete 5.1 Surround configuration.

Figure 8.14. The ITU-R specifications for 5.1 mixing environments. The geometry of placement of a 5.1 Surround configuration has been specified in this setup.

NOTE

DOLBY STEREO VS. DOLBY DIGITAL OR 5.1

The Dolby Laboratories reference material (found at www.dolby.com) suggests that surround speakers not be aimed directly at the listening position but rather to a point that is approximately two feet above that position and mounted higher than the front speakers if mixing material that is to be encoded in the Dolby Surround protocol. Dolby Surround differs from Dolby Digital and 5.1 in that there is only one surround channel. When mixing a Dolby Digital or 5.1 Surround with two surround channels, all of Dolby's recommendations follow that of the ITU-R specification.

NOTE

WHAT IS ITU-R?

The International Telecommunications Union (ITU) is an organization that coordinates government and private sector management of telecom and network services. The "R" refers to the Radio Communications Sector.

Subwoofer and Low-Frequency Effects (LFE) Channel

The subwoofer is perhaps the most difficult speaker to place properly in a mixing room. As low-frequency information is not very directional in nature, the position of the subwoofer does not necessarily have to be in the center of the front speaker array. Placement of speakers should be based on the acoustics of the room to provide accurate frequency response from the subwoofer.

Figure 8.14 shows the typical placement of the subwoofer just off-center and behind the front speaker array. A practical technique for placing the subwoofer is to initially put the subwoofer at the mix position. Then while playing program material that has a significant amount of low frequency information, walk around the room until you find the most pleasant and accurate low-frequency sound. Place the subwoofer there. This process is more accurately done with pink noise and an RTA analyzer. Now, when you're sitting at the mix position, you should hear the same type of response. Subwoofers will excite the low-frequency room modes, and unless acoustic treatment has been applied professionally, there will always be some anomalies in the low-end response of any small mixing room. Placing the subwoofer a great distance away from the other speakers can cause some phase problems with signals that are sent to both the LFE channel and another speaker in the array. Even small changes of a foot or so in subwoofer placement can dramatically affect the response of the system. Try lots of different positions until you find one that is most satisfying .

NOTE

BASS MANAGEMENT AND SUB POSITION

Before you determine the position of your subwoofer, refer to the bass management section later in this chapter. Bass management can affect the relative level between the subwoofer and the other speakers. Your system must be properly set up before you can accurately determine the bass response of your subwoofer's position.

Loudness Calibration

When mixing for film or television, the level at which your monitor is set can drastically affect the outcome of your mix. Theaters have calibrated playback systems that are designed to reproduce a wide frequency range. The levels you generate during your mix session should be faithfully reproduced in theaters due to this calibration. If your mixing system is not calibrated to the same reference points, there is no way of telling how it will be reproduced in the theater. Similarly, television requires a slightly different reference point due to the nature of home viewing. Listening levels in the home are lower than those in the theater. As such, your mixing system should be calibrated to this lower volume in order to create a mix that will translate well into the home listening environment.

Calibration of the playback system involves pink noise that can be generated by the Signal Generator plug-in in Pro Tools. You also need an SPL meter, such as the one pictured in Figure 8.15. A pink noise signal will be generated at the reference operating level of your system, in this case -20dBFS. This is the standard digital reference level in the industry. Calibrate this signal at a certain volume in the mix room so that it will correlate to the same volume when the material is reproduced later. The SPL meter is used to measure the acoustic output of each speaker channel in order to adjust a gain stage in the monitor chain to the correct volume in the room.

Figure 8.15. The Radio Shack SPL meter. This common and relatively inexpensive meter can be used to accurately calibrate your surround speaker system. This one is set up for C weighting , with a slow response. Any decent recording studio should own one of these meters .

NOTE

TRUE PINK NOISE AT -20DBFS RMS?

Some people have questioned the accuracy of the pink noise generated by Digidesign's Signal Generator plug-in. The key to proper calibration of your studio starts with proper test tones. A highly respected collection of test tones developed by Tomlinson Holman (creator of THX), including a tutorial for its use, is available for a modest investment. Most basic calibrations can be accomplished using only the Radio Shack SPL meter. There is also a professional edition with many other tests and complete documentation. If you are serious about calibration (and you should be) owning one of these is a must.

NOTE

- 20DBFS RMS AND 0VU REFERENCE LEVELS

In the old analog days, VU (Volume Units) meters were used to calibrate levels. The nominal recording and playback level was set at 0VU. The VU meter is a slower- reacting meter that does not respond to transient signals. As a result of this response, VU meters more accurately reflect the average level of a signal, or RMS (Root Mean Square), value.

When creating test signals, the average or RMS value of the signal is the most significant. That is why 0VU is used to define the reference or average level of a system. Signals can exceed this 0VU amount to a certain degree without creating distortion. This is the headroom of a given system.

With digital systems, all levels are absolute. Levels are measured in decibels at digital full scale, or dBFS. The maximum level any digital signal can reach is 0dBFS. The nominal, or 0VU level, in digital systems had to be set lower than 0dBFS so there would be headroom available for transient signals to use. This point was set at -20dBFS, leaving 20 decibels of headroom above the nominal operating level before distortion.

When calibrating signal levels, be sure to set any meter you are using to a VU or RMS type of response. Peak meters will register higher levels than a VU meter for the same signal.

Metering is a subject unto itself. A basic audio handbook can give much more detailed information on this subject.

Film-Style Mixing

Film-style mixing requires a slightly different calibration than when mixing for television or home theater applications. All calibration tests will use the pink noise signal at -20dBFS. Here are the steps:

Create the test signal using the Signal Generator setup, as shown in Figure 8.16. Create a tone that is five to ten seconds long that you can loop for continuous playback. Or, you can use test tones from a reference CD such as Tomlinson Holman's TMH Digital Audio Test and Measurement Disc Series, available from www.HollywoodEdge.com.

Figure 8.16. Signal Generator set up to create a pink noise signal at -20dBFS. Make this signal five to ten seconds long in order to loop it for continuous playback.
Route that track to the first channel you wish to calibrate. In this example, we will start with the center channel. Simply assign the track directly to the center channel's output. Figure 8.17 shows the direct routing of the test track to the center channel.

Figure 8.17. Routing of the test track to the center channel speaker only. Each speaker is tested independently.
Set Loop Playback mode to play the test signal repeatedly. Hit play.
Place the SPL meter right at the mix position at head level. If you're holding the meter in your hand, keep it at arm's length distance to avoid coloration from sound reflected off of your body. Also, hold the meter at a slightly upward angle of roughly 45 degrees. Use this meter position to calibrate all the speakers. If possible, use a microphone stand to hold the SPL meter.
Using the SPL meter setup for C weighting and slow response (Figure 8.15), adjust your monitor level until you get a reading of 85dBC (the C stands for C weighting of the meter).
Repeat this for both left and right speakers. All front three speakers are calibrated to the same level.
When calibrating the surround speakers, set the individual monitor volume to get a reading of 82dBC. With film mixing, set the surround speakers at a slightly lower volume. If you're holding the meter in your hand, turn your back 90 degrees towards the speaker you're calibrating so as to avoid obscuring the sound from it with your body. Aim the meter at the wall closest to the surround speaker you are calibrating.
LFE level adjustment is more complex. To properly calibrate the volume of the LFE channel, you must have a real-time analyzer. However, a simple SPL meter can work in a pinch . For film mixing, the LFE channel will play back 10dB louder than any of the front three speakers for the same input level. The reason for this is to give the LFE channel more headroom for low-frequency sounds such as explosions. Signals sent to the subwoofer should be band -limited from 25 to 120 Hz. When using a simple SPL meter, it should read about 89dBC when feeding pink noise at an RMS level of -20dBFS. Due to the C weighting of the SPL meter and the limited bandwidth of the subwoofer, this level will not quite reach the 10dB increase specified. It is an approximation and can be more accurately determined with a real-time analyzer (RTA).

NOTE

ADJUSTING VOLUME

When calibrating reference levels for any speaker, the adjustments should be made so as not to affect the level of a Pro Tools output path directed to that speaker channel. Otherwise, if you make playback monitor calibration adjustments within Pro Tools you will be calibrating your recording levels to your speakers and not your speakers to a reference recording or output level, thereby throwing away the benefits of calibration: accurate reproduction of your mix on other calibrated playback systems. The level adjustment should be made outside of the mixing environment. Using the volume knobs on your power amps is a very effective way of adjusting the volume and also maintaining the highest degree of signal to noise ratio in the playback system.

TV and Home Theater Applications

When mixing material for television, each speaker, including the surrounds , is calibrated to a reference level of 79dBC. This is due to the lower average listening level used by consumers. Referencing at this lower level will provide a better dialog mix for in-home viewing. The subwoofer should be calibrated 10dB higher, just the same as in theatrical mixing.

NOTE

SURROUNDS IN A SMALL ROOM

It should be noted that when you are mixing in a very small room where the surround speakers are less than six feet away, they should be turned down 2dB to compensate for their close proximity to the mix position. This method has proven to be very effective when mixing on location in a remote truck where space is definitely limited.

Bass Management

OK, this gets complicated. The reason we need a bass management system is because many consumer systems use five small satellite speakers combined with a subwoofer to supplement the low frequency response of the system and act as the LFE channel. The low-frequency information that is directed to any of the five satellite speakers, but cannot be reproduced by them, is redirected by the bass management system to the subwoofer. Since lower-frequency sounds are less directional, the spatial image does not suffer.

The amount and crossover frequency at which this redirection of low-end occurs is fairly standard among consumer playback systems. Typically, the crossover frequency is 80Hz, meaning that frequencies below 80Hz in any channel will be diverted to the subwoofer.

NOTE

THEATRICAL SOUND SYSTEMS

Sound systems in movie theaters do not have or use bass management. The front three speakers are full-range and can handle deep bass. The surround speakers are full-range as well, but they typically are not as powerful. The subwoofer in theaters reproduces signals only from the LFE channel. No signals from any other channels will come through the subwoofer. Consumer systems use bass management for economic and aesthetic reasons, not sonic integrity. 5.1 Surround is best heard with five full-range speakers and a dedicated LFE subwoofer.

Bass management can also be used to enhance the performance of smaller speakers used in the studio. Many times, studios will purchase surround and sometimes center speakers that are smaller than the main left and right ones and, thus, are ill-equipped to handle lower frequencies. This is usually due to budgetary considerations, as the cost of a full-range 5.1 Surround speaker system can be formidable. Bass management can compensate for the low-frequency response of the smaller speakers by redirecting the low-end to the subwoofer channel. If you must use some smaller speakers in your system, make them the surrounds and try to keep the left, center, and right speakers matched in response and size.

In addition to this low-frequency content from the five satellite speakers, the subwoofer must also reproduce the signals for the LFE channel. For film mixing, the LFE channel must be regarded as a separate entity from the low-frequency content of the bass management redirection. Even though these two signals will be reproduced by the subwoofer, they must be treated independently, as two discrete sources.

The way you treat the two signals as two separate sources is through the use of a bass management system while you are mixing. Waves offers the 360 degree Surround Toolkit, which, among many other tools, has a bass management plug-in that can be used on the master fader to assist in calibrating your system with bass management. There are other software and hardware solutions for bass management, but I will use the Waves plug-in as a common example.

As bass management is basically acting as a home-theater emulation system, it should be used as the last item in your signal path. Consider it a part of your speaker system. And, as you never record the mix you create by miking the speakers, you must disable any bass management before you record your mix. Recording with bass management on will yield unpredictable results based solely on your mixing environment and not the real world.

NOTE

DISABLE BASS MANAGEMENT WHEN PRINTING FINAL MIXES !

All bass management does is calibrate your speakers so that they react like a home theater system; it does not encode or decode any Dolby or other surround information. It should not exist in the audio mix going to tape or disk, only in the room's monitor path.

Calibration

Using the Waves M360 plug-in shown in Figure 8.18, I will outline how to calibrate the bass management system. It is similar to the calibration steps outlined earlier in this chapter, with certain exceptions. The plug-in has the ability to divide each channel into frequency bands and divert the low-frequency band to the subwoofer. The amount of signal that goes to the Sub channel can be varied independently for each channel. The crossover frequency and slope of the filter used to divide the signals is also adjustable. The LFE, or .1 channel of a 5.1 surround mix, is dealt with separately from this bass management redirected signal. The result is that the subwoofer will act as the low-frequency driver for each speaker in the system in addition to providing discrete LFE signals.

Figure 8.18. The All button will engage all the high and low pass filters, thereby directing all low frequency energy to the subwoofer. For custom setups, individual channels can be filtered without affecting the others. This can be helpful when you have one pair of speakers that are full range and several others that require bass enhancement.

Here's how to calibrate the bass management system:

Set the crossover frequency to 80Hz. This is also the default setting. The default setting for the slope of this crossover filter is set to 24dB/octave for the subwoofer channel and 12dB/octave for all satellite channels, as shown in Figure 8.18. This setting should be fine for most situations. If your satellite speakers are particularly small, you might have to use a higher crossover frequency so that all of the low-end that is missing from the satellites is present in the subwoofer. Experiment to find the best setting for your speakers.
Engage the high and low pass filters on every channel by clicking the All button, as shown in Figure 8.18.
Place a multi-mono instance of the Signal Generator plug-in on the surround master channel ahead of the bass management plug-in. Set it for pink noise at the reference level of -20dBFS. This will provide a continuous pink noise signal to all speaker channels.
Using the solo buttons on each satellite channel, proceed with the calibration setup as outlined earlier in this chapter. There are some additions and changes to the procedure that relate specifically to the subwoofer channel.
When you've calibrated the volume for all five of the satellite speakers to 85dBC, mute every one except the center channel, as shown in Figure 8.19.

Figure 8.19. Mute buttons are engaged on every satellite channel except the center.

NOTE

CALIBRATE ONE SPEAKER AT A TIME

Remember that when you're calibrating, you should hear only one speaker at a time. If you hear more than one speaker, your meter reading will be inaccurate. The Waves plug-in provides convenient mute and solo switches to help in this process.
Solo the Sub channel, as shown in Figure 8.20. Make sure you don't accidentally solo the LFE channel instead. Remember, the Sub channel and the LFE channel are two distinct signals, even though they're both reproduced by the subwoofer speaker.

Figure 8.20. Solo the Sub channel, not the LFE channel above the Sub. With all but one satellite speaker muted, the Sub channel will contain only the low-end content from the unmuted satellite speaker. The Sub channel should be calibrated 6dB less than the satellite speaker. Usually this is 79dBC.
With only one satellite speaker unmuted, adjust the Send To Sub control, shown in Figure 8.20, to get a meter reading 6dB lower than its corresponding satellite channel (79dBC if using 85dBC as reference). The 6dB difference is due to the fact that the Sub channel contains fewer frequency bands and is therefore not as loud.
Repeat this Sub channel calibration process for each satellite speaker.
Next, mute the Sub channel and all satellite channels.
Solo the LFE channel and set the LFE Adjust to +10dB. This adjusts the LFE channel for film mixing, which is 10dB louder than the other speakers.
Using the LFE Gain adjustment, shown in Figure 8.21, calibrate the level to somewhere between 89 and 92dBC. Again, the SPL meter will not be as accurate as a RTA when calibrating just the low-frequency subwoofer. Some experimentation might be necessary.

Figure 8.21. With the LFE adjust set to + 10dB, use the LFE Gain adjustment to fine-tune the calibration for an SPL meter reading of somewhere between 89 and 92dBC. Make sure to use the slow mode on the SPL meter, as it will swing back and forth when registering low-frequency signals. Use the middle point of the swing as your true reading.
Turn off the pink noise generator and un-mute every channel. You should be ready to go.

Time Alignment

The Waves M360 plug-in is capable of meeting other calibration needs as well. In some studio situations it's not possible to have all speakers at the same distance from the mix position. In these cases, it will be necessary to use time delays to properly align the speakers so that sounds from different speakers will arrive at the listener at the same time. A common situation is having the center speaker forward from the left and right speakers due to soffit mounting of the main speakers, or perhaps placement of a viewing screen, as seen in Figure 8.22.

Figure 8.22. The center channel speaker is forward of the main left and right speakers and, therefore, sound from the center speaker will arrive earlier than sound from the left and right speakers.

The solution to this problem is to apply a small delay to the signal being sent to the center speaker so that sound from it arrives at the same time or "in phase" with sounds coming from other speakers. Use a tape measure to calculate the difference in distance between the two speakers. Knowing that sound travels at roughly one foot per millisecond, you can calculate the approximate delay needed to align the speakers.

Let's say the center channel speaker is one foot closer to the listener than any of the other speakers. This means that a delay of one millisecond is to be applied to the center channel in order to align it with the other speakers. The Waves M360 plug-in provides a delay adjustment for each speaker to accommodate this, as shown in Figure 8.23. In this example, the setting of one millisecond would correct the problem. This adjustment goes down to tenths of a millisecond for very precise adjustment of speaker alignment; this is necessary in order to maintain an accurate sound field in which to mix.

Figure 8.23. The channel delay adjustment in M360 is used to compensate for speakers that are not physically aligned properly. Here, the center channel has been delayed by one millisecond to compensate for the position shown in Figure 8.22, which is one foot closer than the other speakers.

The M360 plug-in has several other parameters that work in conjunction with the Waves surround panners and imagers used on individual channels. These parameters can control the imaging of sounds within the surround field. Suffice to say, many interesting effects can be achieved through the use of these parameters, but they are beyond the scope of this book. Refer to the Waves literature for more details.

NOTE

ANSI/SMPTE 202M X-CURVE

In large theater-size mixing rooms, or dub stagesthose larger than 5300 cubic feetan EQ curve is applied to the speakers to compensate for the sound's interaction with the room itself. In smaller mixing rooms (less than 5300 cubic feet) where material is mixed that will be played back in larger rooms such as movie theaters, a modified X-Curve 222M is applied to help mixes translate well to these larger spaces. The application of room EQ in this manner is complex and opinions vary among acousticians as to the best methods . More information is available at www.dolby.com. I would advise consulting with an acoustician when setting up a mix room for film, TV, or DVD mixing.

[ LiB ]

Preparation for Mixing